Manufacture of most metal products typically requires various forming and folding operations of metal foils or sheets, and numerous types of equipment are known in the art to perform such tasks. Unfortunately, most of the known metal forming devices and methods have numerous disadvantages or are not even capable of hemming where the edge of one or more pieces of metal are folded back onto themselves. To circumvent such difficulties, specialized equipment can be used.
For example, a series of wheels can be employed to sequentially form a hem as described in GB 2 403 924. Alternatively, where wheel operation is not desirable or impractical, single die devices with a curved die surface can be used as taught in U.S. Pat. No. 7,204,118. However, such devices typically require an already angled sheet. Similar difficulties arise with devices as shown in EP 1 503 873 B1 where a preformed die with a curved surface is used to guide edge movement and where a second die is used to flatten the hem. In still other known methods, a compound flanging and hemming die is employed to hem two sheets together as shown in U.S. Pat. No. 5,454,261.
Alternatively, one or more rotary bending tools can be employed as depicted in U.S. Pat. No. 5,404,742, and U.S. Pat. No. 3,071,176 discloses a folding machine in which the leading portion of a metal sheet is first pressed into an angled groove to form a partially folded edge that is then completely folded via an anvil. Alternatively, dual moving elements may are used to hem sheets of metal as described in U.S. Pat. No. 6,079,250.
While such devices are often satisfactory for their relatively specialized tasks, they tend to lack satisfactory performance where metal foil encapsulated insulation products are produced that require hemming of edges that are often not straight. Moreover, additional difficulties are found where the metal edge that is to be hemmed is directly adjacent to the body of the work piece. In such cases, folding or hemming is most commonly performed using a pair of pliers, which is not only extremely difficult and time consuming, but also impedes efficient production flow.
Thus, even though numerous metal forming devices are known in the art, there is still a need to provide improved devices and methods for hemming, especially where edges are curved and/or where the hem is in close proximity to the work piece.